Metal alkoxides and aryloxides are typically produced by reaction of the metal, or its halide with the respective alcohol, aryl hydroxy compound or the corresponding salt, as illustrated in the following three reactions: ##STR1##
The pure metal, in all cases, is produced by high temperature (&gt;900.degree. C.) metallurgical processes or electrochemical processes as described in The Production of Inorganic Materials, by J. W. Evans and L. C. De Jonghe, MacMillan Pub. Co., N.Y., N.Y., 1991. The chlorides can be made via several routes as illustrated by the following three reactions: ##STR2##
Before any metal alkoxides can be prepared, production of the starting reactants requires high temperature, energy and equipment intensive steps. The chloride routes also require toxic and polluting reactants which mandate the use of specially designed reactors. Moreover many simple alkoxides, for example Al(OCH.sub.3).sub.3 or Al(OCH.sub.2 CH.sub.3).sub.3, form poorly tractable polymers [see Advanced Inorganic Chem., Cotton and Wilkinson, Wiley Interescience, 5th Ed., 1988, pp. 220-1] that are difficult to handle because they are very moisture sensitive, corrosive, highly flammable and/or toxic.
Thus, typical routes to simple metal alkoxides are multistep and require excessive temperatures that waste energy and specially designed, high cost equipment. Furthermore, many of the resulting compounds are difficult to work with because of their instabilities and toxic nature.
The preparation of double alkoxides is even more complicated, as described in Metal Alkoxides, D. C. Bradley, R. C. Mehrotra, D. P. Gaur; Academic Press, N.Y., N.Y. (1978). Examples of double alkoxides made from metal derived alkoxides include: (1) "Erste Kristallstruktur eines gemischten Al-Mg-Alkoholates," J. Sassmannshausen, R. Riedel, K. B. Pflanz, H. Chmiel, Z. Naturforsch. (1993) 48b, 7-10, and (2) "Heterometallic Aluminum Alkoxides. The Characterization of {Mg[Al-(OPr.sup.i).sub.4 ].sub.2 } and Mg.sub.2 Al.sub.3 (OPr.sup.i).sub.13," J. A. Meese-Marktscheffel, R. Fukuchi, C. M. Jensen, J. W. Gilje, Chem. Mater. (1993), 5, 755-757. The latter paper demonstrates that attempts to prepare pure Mg/Al double alkoxides via reaction (7) can lead to a mixture of products with variable stoichiometries: EQU Mg(OPr.sup.i).sub.2 +Al(OPr.sup.i).sub.3 .fwdarw.Mg[Al(OPr.sup.i).sub.4 ].sub.2 +Mg.sub.2 Al.sub.3 (OPr.sup.i).sub.13 ( 7)
Mixtures of compounds and off stoichiometric compounds make processing single phase ceramics from precursors quite difficult because the processing variables can be extremely different. Furthermore, although the use of isoproxide or sec-butoxide (OBu.sup.i) groups is necessary to avoid the formation of intractable polymers, these groups are much less preferable than MeO-- or EtO-- groups for use in preceramic polymers. This is because they contain significant quantities of carbon that must be effectively removed to form pure oxide ceramic or glass products. The potential to incorporate carbon impurities increases with increasing carbon content. Taken as a whole, monofunctional alcohol based alkoxides (e.g. OPr.sup.i ligands) are not particularly useful for preceramic polymer processing; however, the alternative, use of methoxide or ethoxide ligands is also not useful because these ligands lead to the formation of intractable polymeric precursors that cannot be further processed to useful shapes.
Cruickshank et al [a. M. C. Cruickshank, L. S. D. Glasser, "A Penta-co-ordinated Aluminate Dimer; X-ray Crystal Structure," J.C.S. Chem. Comm. (1985) 84-85. b. M. C. Cruickshank, L. S. D. Glasser, S. A. I. Barri, I. J. F. Poplett, "A Penta-co-ordinated Aluminum; a Solid-state .sup.27 Al NMR Study," J.C.S. Chem. Comm. (1986) 23-24.] teach the synthesis of a dimeric, pentacoordinate barium aluminum alkoxides from metal derived alkoxides: ##STR3##
This crystalline material is not processable to any useful shape, e.g. fibers or free standing films.
An alternate approach to these materials, directly from the corresponding metal oxides or hydroxides, offers an opportunity to develop low cost, low polluting, and lower energy routes to these materials as well as novel materials without the limitations described above. For example, the reaction of silica with an alkali salt of catechol provides access to the tris(catecholato) silicate: ##STR4##
This reaction was first reported by Rosenheim et al [Rosenheim, A.; Raibmann, B. and Schendel, G.; Z. Anorg, Chem., 1931, 196, 160.]. Laine et al have also described the preparation of penta-and hexaalkoxysilane anions and dianions. See "Silicon and Aluminum Complexes", R. M. Laine, K. A. Youngdahl and P. Nardi, U.S. Pat. No. 5,099,052 Mar. 24, 1992; "Silicon and Aluminum Complexes", R. M. Laine, K. A. Youngdahl, U.S. Pat. No. 5,216,155, June 1993; "SiO.sub.2 as a Starting Material for the Synthesis of Pentacoordinate Silicon Complexes. I.," K. Y. Blohowiak, D. R. Treadwell, B. L. Mueller, M. L. Hoppe, S. Jouppi, P. Kansal, K. W. Chew, C. L. S. Scotto, F. Babonneau, J. Kampf, R. M. Laine, Chem. Mater. (1994) 6, 2177-2192; R. M. Laine, K. Y. Blohowiak, T. R. Robinson, M. L. Hoppe, P. Nardi, J. Kampf, and J. Uhm, "Synthesis of Novel, Pentacoordinate Silicon Complexes from SiO.sub.2," Nature (1991) 353, 642-644; "Barium Tris(glycolato)silicate, a Hexacoordinate Alkoxy Silane Synthesized from SiO.sub.2. " M. L. Hoppe, R. M. Laine, J. Kampf, M. S. Gordon, L. W. Burggraf, Angew. Chem. Int. (1993) 32, 287-289; and "Group II Tris(glycolato)silicate Precursors to Silicate Glasses and Ceramics," P. Kansal, R. M. Laine, J. Am. Ceram. Soc. in press. All of these compounds are also crystalline solids that are not further processable to useful shapes.
A reaction related to (8) but involving Al.sub.2 O.sub.3 was described by Laine et al [Silicon and Aluminum Complexes, R. M. Laine, K. A. Youngdahl, P. Nardi, U.S. Pat. No. 5,099,052 Mar. 24, 1992]: ##STR5##
The material, which was poorly described, suggests the formation of a trianionic hexacoordinated monomer using a diol reactant.
In all instances, the above cited studies teach only the synthesis of mono or dianionic silicates, monoanionic and trianionic aluminates and one example of a dimeric aluminate species, all based on simple mono or difunctional alcohols (diols). In all instances, the counterion is a group Ia or IIa metal. In all instances, the products are crystalline and do not offer useful viscoelastic properties necessary for forming useful shapes.
In no instance does the prior art teach a commercially viable preparation of processable polymers containing mixed anionic/neutral monomer units in the polymer backbone or the use of triols or higher "ols" for the formation of double alkoxides, especially double alkoxide oligomers and polymers, and particularly from SiO.sub.2, Al.sub.2 O.sub.3 or Al(OH).sub.3. Furthermore, none of the above cited studies teach the use of nitrogen containing triols or higher "ols" as a means to stabilize the double alkoxides to reduce moisture sensitivity, improve processability and minimize carbon content when used as preceramics.
U.S. Pat. No. 2,881,198 to D. Bailey and F. O'Connor taught that reacting silica with a catalytic amount of alkali metal hydroxide under conditions that remove water by distillation or azeotrope (often under pressure) leads to the synthesis of monomeric, neutral alkoxy silanes. However, the disclosed reaction was extremely slow, requiring days to complete. Furthermore, the yields obtained were only 50-78%, as the alkali base catalyst eventually reacted with the SiO.sub.2 to produce alkali silicate byproducts.
Fry appeared to teach that silicic acid will react with a large excess of triethanolamine (TEA) to produce water and what was described as a "more or less nondescript silatrane material". Although the reaction which accompanied this disclosure incorrectly characterized the formula for silicic acid, the synthesis was predicated upon the use of TEA as the sole solvent. Also, the uncharacterized product appears to be a relatively low molecular weight species. See Frye et al., "Pentacoordinate Silicon Compounds. V. Novel Silatrane Compounds," J. Am. Chem. Soc. (1971) 93, 6805-6811.
Struchkov et al. [V. E. Shklover, Yu. T. Struchkov, M. G. Voronkov, Z. A. Ovchinnikova, V. P. Baryshok, "Crystal and Molecular Structure of the Unusual Alumatrane Complex: [Al(OCH.sub.2 CH.sub.2).sub.3 N].sub.4. 3HOCH (CH.sub.3).sub.2. 0.5C.sub.6 H.sub.6," Dokl. Akad. Nauk SSR (1984) 227, 1185-9. Chem. Abstracts, (1984) 102: 37181k.], teach the synthesis of [Al(TEA)].sub.4. 3HOCH(CH.sub.3).sub.2.0.5C.sub.6 H.sub.6, by reaction of TEA with Al(OPr.sup.i).sub.3 in benzene. The product is not solvent free which will affect its properties (e.g. benzene is toxic, it causes leukemia) and was not made from Al.sub.2 O.sub.3 or Al(OH).sub.3. More recently, work by Verkade et al [Inorg. Chem. (1993) 32, 2711] confirms the Struckhov synthesis. Neither of these works describe the synthesis of anionic compounds or anionic/neutral oligomers and polymers.